18F-FDG or 3'-deoxy-3'-18F-fluorothymidine to detect transformation of follicular lymphoma.

UNLABELLED Considering the different treatment strategy for transformed follicular lymphoma (TF) as opposed to follicular lymphoma (FL), diagnosing transformation early in the disease course is important. There is evidence that (18)F-FDG has utility as a biomarker of transformation. However, quantitative thresholds may require inclusion of homogeneous non-Hodgkin lymphoma subtypes to account for differences in tracer uptake per subtype. Moreover, because proliferation is a hallmark of transformation, 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) might be superior to (18)F-FDG in this setting. To define the best tracer for detection of TF, we performed a prospective a head-to-head comparison of (18)F-FDG and (18)F-FLT in patients with FL and TF. METHODS (18)F-FDG and (18)F-FLT PET scans were obtained in 17 patients with FL and 9 patients with TF. We measured the highest maximum standardized uptake value (SUVmax), defined as the lymph node with the highest uptake per patient, and SUVrange, defined as the difference between the SUVmax of the lymph node with the highest and lowest uptake per patient. To reduce partial-volume effects, only lymph nodes larger than 3 cm(3) (A50 isocontour) were analyzed. Scans were acquired 1 h after injection of 185 MBq of (18)F-FDG or (18)F-FLT. To determine the discriminative ability of SUVmax and SUVrange of both tracers for TF, receiver-operating-characteristic curve analysis was performed. RESULTS The highest SUVmax was significantly higher for TF than FL for both (18)F-FDG and (18)F-FLT (P < 0.001). SUVrange was significantly higher for TF than FL for (18)F-FDG (P = 0.029) but not for (18)F-FLT (P = 0.075). The ability of (18)F-FDG to discriminate between FL and TF was superior to that of (18)F-FLT for both the highest SUVmax (P = 0.039) and the SUVrange (P = 0.012). The cutoff value for the highest SUVmax of (18)F-FDG aiming at 100% sensitivity with a maximum specificity was found to be 14.5 (corresponding specificity, 82%). For (18)F-FLT, these values were 5.1 and 18%, respectively. When the same method was applied to SUVrange, the cutoff values were 5.8 for (18)F-FDG (specificity, 71%) and 1.5 for (18)F-FLT (specificity, 36%). CONCLUSION Our data suggest that (18)F-FDG PET is a better biomarker for TF than (18)F-FLT PET. The proposed thresholds of highest SUVmax and SUVrange should be prospectively validated.